1. Field of the Invention
This invention relates to a liquid crystal optical element of a transparent and scattering type for controlling a near infrared ray laser beam and a laser projection apparatus employing the liquid crystal optical element.
2. Discussion of Background
As a projection apparatus employing a YAG laser, there are, for instance, a laser material processing apparatus for working an object, a marking apparatus for marking characters or figures, and the like, which are widely used. As the conventional technology, an apparatus for performing mechanical scanning by employing a scanner, an apparatus employing a fixed mask of a metal or the like, an apparatus employing a conventional twisted nematic (TN) type liquid crystal optical element as a mask and the like are pointed out.
For example, a transparent type liquid crystal element having polarizing plates and a laser marker which irradiates a laser beam reflected with a pattern information of the transparent type liquid crystal element on an object to be worked, are disclosed in Japanese Unexamined Patent Publication No. 11088/1989 (corresponding to U.S. Pat. No. 4,818,835).
Further, a laser marker employing an STN liquid crystal mask is described in Japanese Unexamined Patent Publication No. 241681/1990.
A laser marker provided with polarizers and optical fibers is described in Japanese Unexamined Patent Publication No. 193281/1991.
A laser marker which is characterized in that the laser marker is provided with both a fixed display portion and a liquid crystal performing variable display, is described in Japanese Unexamined Patent Publication No. 264178/1991.
A laser marker apparatus has recently been known which employs a transparent and scattering type liquid crystal optical element having an operational mode which is different from those of the above.
For instance, a laser letter marking apparatus employing a transparent and scattering type liquid crystal mask is described in Japanese Unexamined Patent Publication No. 180285/1991. Further, a laser marking apparatus employing a scattering type liquid crystal is described in Japanese Unexamined Patent Publication No. 241683/1992. However, there is no detailed description on the inner structure of a scattering type liquid crystal optical element in the laser letter marking apparatus.
In the conventional technology it is extremely difficult to mark arbitrary figures or characters, or work an arbitrary portion of object, and the laser marker apparatus is complicated by itself. In case of employing a TN type liquid crystal optical element, the arbitrarily of the apparatus is improved by controlling the switching-on and the switching-off of the respective pixels.
However, since two sheets of polarizer are employed in the TN type liquid crystal optical element, the coefficient of utilization of laser beam is low. Accordingly, the conventional technology has such drawbacks in that the sheets of polarizer are heated and are apt to be deteriorated by intensifying the laser beam.
A guest/host (GH) type liquid crystal optical element may be employed to cope with the drawbacks. However, the GH type liquid crystal optical element has the disadvantage of insufficient ON/OFF contrast ratio.
A system is proposed which employs a mask of a transparent and scattering type liquid crystal optical element which employs a liquid crystal and solidified matrix composite wherein liquid crystal is dispersed in a matrix. This transparent and scattering type optical element is provided with an advantage wherein the coefficient of utilization of laser beam is high and a high contrast ratio can be provided.
However, when the conventional liquid crystal and solidified matrix composite which is employed in the application in use of visible light wavelength region, is simply utilized, a characteristic thereof (such as threshold value characteristic) at the wavelength of near infrared ray, that is employed, is not sufficient, it is difficult to form a high density information at one time by a time-sharing (multiplexed) driving, and, therefore, a high processing and marking characteristics has not been achieved.
The multiplex driving is an indispensable driving method in forming an image by employing a number of pixels. The multiplexed driving is necessary even in case of low pixel numbers, for instance, in a 36.times.36 dots matrix, since the pixel number is 1296, and 1297 terminals are required in the static driving. By contrast, in the multiplexed driving, only 650 terminals are required in case of 1/2 duty, and 328 terminals, in case of 1/4 duty.
However, in case of forming electrodes to perform the multiplex driving, when the pixel number exceeds a certain value, there causes inevitably overlapped portions wherein lines of segment electrodes and lines of common electrodes are overlapped. These overlapped portions of electrodes adversely influence a projected image.